1. Field of the Invention
This invention relates to the mechanical arts. In particular, it relates to an improved passenger lift integrating safety features.
2. Discussion of the Prior Art
There is an increasing sensitivity to the need for facilitating the mobility of all members of our society, including people who have difficulty in walking and people who use wheelchairs. Such people often have difficulty moving between different levels, such as getting into and out of vehicles and using stairways. Consequently, there is a great need for passenger lifts to transport people into and out of vans and buses and between the floors of buildings.
Passenger lifts, per se, are well known in the art. Representative passenger lifts are described in U.S. Pat. Nos. 4,534,450 and Re. 31,178. To be effective, passenger lifts must be reliable, cost effective and, most importantly, safe.
Among the various types of safety features which have been included in wheelchair lifts are restraining devices, such as restraining belts and barrier plates -plates attached to the sides and ends of a lift platform, perpendicular to the platform's surface. These restraining devices help prevent wheelchairs from rolling off lifts when the lifts are in operation.
For example, U.S. Pat. No. 4,726,730 discloses an assembly for lifting and tilting a wheelchair. The wheelchair and its passenger are held in place by safety belts passing along platform sides and over the wheelchair and its occupant. Ricon Corporation, Pacoima, Calif. offers wheelchair lifts incorporating restraining belts extendable between a pair of handrails and barrier plates along the front and side edges of the lifts' platform. U.S. Pat. No. 5,026,244 discloses a wheelchair lift having both a retention strap, drawn across the front of a wheelchair and attached to a handrail, and a barrier plate positioned at the front edge of the platform.
U.S. Pat. No. 5,052,521 discloses a stairway lift accommodating either a wheelchair or a fixed seat. The lift contains two guard arms lowered during operation and three platform flaps raised during operation. The distal end of each guard arm is provided with an inwardly directed right angle bend, such that a rigid, substantially rectangular, outer perimeter is formed by the arms in conjunction with the lift's vertical housing when both arms are in their lowered position.
Barrier plates and other restraining devices automatically deployed during the operation of a lift are known in the art. For example, U.S. Pat. Nos. 3,651,965, 4,133,437, 4,442,921 and 5,040,936 disclose lifts having barrier plates automatically raised into place, when the lifts are in operation. U.S. Pat. No. 4,457,402 discloses a wheelchair lift having an automatic mechanism for moving power safety gates from their open to their closed positions, when the platform is deployed.
Barrier plates which must be in place in order to operate a wheelchair lift are also known in the art. U.S. Pat. Nos. 4,479,753 and Re. 33,595 disclose movable barrier plates, placed in their upright position before the platform will move up or down. U.S. Pat. No. Re. 33,595 describes a safety barrier switch triggered when the safety barrier is raised.
U.S. Pat. No. 4,420,286 discloses vehicles outfitted with wheelchair lifts. The lifts have several interlock switches to prevent operation of the lift in the event the vehicle transmission is not in "park", or a manually operable arming switch is not closed, or a safety flap mounted on the loading platform is not in an up position, or the platform is not in its fully projected position.
U.S. Pat. No. 4,804,308 discloses a wheelchair lift having safety gates actuated by an air cylinder. In the preferred embodiment, interlocks prevent operation of the air cylinder until the platform is deployed.
U.S. Pat. No. 3,651,965 discloses a wheelchair lift having a mainline switch which must be closed before any of the lift's hydraulically actuated functions begin. It is also known to include electric belt interlocks in the seat belts of automobiles. With such interlocks, the automobile cannot be started unless the seat belt is fastened.